Low-resistance and high-tolerance monolithic spiro-bifluorene-based conjugated microporous polymer for co-capture of PM and CO2 in waste gas

Abstract

The utilization of solid adsorbents for the co-capture of harmful particulate matter (PM) and carbon dioxide (CO2) in industrial exhaust streams represents a crucial component within the emerging field of waste gas terminal treatment technologies. Extensive research has focused on particulate or powdered adsorbents rather than monolithic materials, whereas monolithic adsorbents exhibit superior advantages in practical industrial applications. Herein, a monolithic spiro-bifluorene-based conjugated micro-porous polymer (DS-CMPs) with hierarchical porous and functionalized hollow nanotube structures was proposed. The favorable characteristics exhibited by DS-CMPs encompass a highly delocalized π-π conjugated skeleton, permanent porosity, unique thermal and chemical stability, precisely defined chemical composition, and excellent water vapor tolerance. These inherent qualities guarantee that DS-CMPs employed for the co-capture of PM and CO2 from exhaust gases exhibit exceptional capture efficiency, low permeation resistance, favorable isosteric heat of adsorption (Qst), and recyclability. The reasons behind the high capture efficiency and low permeation resistance of monolithic DS-CMPs were analyzed through mechanistic exploration and Electrostatic Surface Potential (ESP) calculations. Moreover, the stability inherent in the framework structure and physicochemical properties of DS-CMPs can surmount the notable decline in the capturing capability of porous materials utilized within damp and elevated temperature surroundings. Following exposure to elevated humidity (RH = 86 ± 1 %) and high-temperature (500 ℃) conditions, DS-CMPs exhibited a remarkable capture efficiency exceeding 99.00 % for PM2.5. The self-assembly of monolithic DS-CMPs into a smooth array of nanotube bundles effectively reduces the friction between airflow and material, enhances airflow dispersion, and achieves a minimum permeability resistance of only 8 Pa. At a pressure of 1 bar and temperature of 273 K, the CO2 adsorption capacity of DS-CMPs amounts to 2.72 mmol/g. The high absorption capacity for CO2 is primarily attributed to the presence of a significant microporous/mesoporous ratio and notable surface charge differences. In contrast to powdered adsorbents plagued by sample elution and gas pressure drop issues, the monolithic DS-CMPs showcases good mechanical properties, rendering them readily applicable within industrial bed circulation systems to achieve the co-capture of PM and CO2.